Medium transport device and image forming apparatus

ABSTRACT

A medium transport device include: an inclination corrector including a first inclination correction member and a second inclination correction member disposed away from each other in a width direction of a medium, the first inclination correction member and the second inclination correction member being individually drivable during transport of the medium, the inclination corrector being configured to correct an inclination of the medium relative to a transport direction of the medium by causing a difference in the transport of the medium between the first inclination correction member and the second inclination correction member; and a medium transporter disposed on a downstream side of the inclination corrector in the transport direction and configured to transport the medium, the medium transporter including a pair of medium transport members disposed across the medium in a thickness direction of the medium, the medium transport members being movable between a transport position where the medium transport members nip and transport the medium and a non-nipping position where a nip of the medium is canceled. During correction of the inclination of the medium by the inclination corrector, the medium transporter is moved to the non-nipping position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2022-052731 filed Mar. 29, 2022.

BACKGROUND (i) Technical Field

The present disclosure relates to a medium transport device and an imageforming apparatus.

(ii) Related Art

Japanese Unexamined Patent Application Publication No. 2008-1473([0036]-[0055], FIGS. 2, 5, 6, 9, 10) describes the following technologyin a medium transport device that transports a medium before or afterimage printing.

Japanese Unexamined Patent Application Publication No. 2008-1473describes a structure including skew correction rollers (21, 22)disposed away from each other in an axial direction and a pair oflateral registration rollers (30) on a downstream side of the skewcorrection rollers (21, 22). In Japanese Unexamined Patent ApplicationPublication No. 2008-1473, in response to a nip of a sheet (S) by theskew correction rollers (21, 22), the lateral registration rollers (30)are separated so as not to nip the sheet (S). The transport speeds ofthe skew correction rollers (21, 22) are varied depending on a skewamount at the leading edge of the sheet (S) to correct the skew of thesheet (S). After the skew has been corrected, the sheet (S) is nipped bythe lateral registration rollers (30) on the downstream side of the skewcorrection rollers (21, 22). After the skew correction rollers (21, 22)have been separated from the sheet (S), the lateral registration rollers(30) move in the axial direction to shift the positions of lateral edgesof the sheet (S) to lateral registration positions.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate tosuppression of damage to a medium in a structure in which mediuminclination correction is performed using a transport speed differenceby independently driving two transport members disposed away from eachother in a width direction of the medium, compared with a case where themedium inclination correction is performed with the medium nipped by amedium transport member on an upstream or downstream side of the twotransport members.

Aspects of certain non-limiting embodiments of the present disclosureaddress the above advantages and/or other advantages not describedabove. However, aspects of the non-limiting embodiments are not requiredto address the advantages described above, and aspects of thenon-limiting embodiments of the present disclosure may not addressadvantages described above.

According to an aspect of the present disclosure, there is provided amedium transport device comprising: an inclination corrector comprisinga first inclination correction member and a second inclinationcorrection member disposed away from each other in a width direction ofa medium, the first inclination correction member and the secondinclination correction member being individually drivable duringtransport of the medium, the inclination corrector being configured tocorrect an inclination of the medium relative to a transport directionof the medium by causing a difference in the transport of the mediumbetween the first inclination correction member and the secondinclination correction member; and a medium transporter disposed on adownstream side of the inclination corrector in the transport directionand configured to transport the medium, the medium transportercomprising a pair of medium transport members disposed across the mediumin a thickness direction of the medium, the medium transport membersbeing movable between a transport position where the medium transportmembers nip and transport the medium and a non-nipping position where anip of the medium is canceled, wherein, during correction of theinclination of the medium by the inclination corrector, the mediumtransporter is moved to the non-nipping position.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present disclosure will be described indetail based on the following figures, wherein:

FIG. 1 illustrates an overall image forming apparatus of a firstexemplary embodiment;

FIG. 2 is an enlarged view of a visible image forming device of thefirst exemplary embodiment;

FIG. 3 illustrates a medium transport device of the first exemplaryembodiment;

FIG. 4 illustrates a positional relationship between a positionalcorrector and an inclination corrector of the medium transport device ofthe first exemplary embodiment;

FIG. 5 illustrates a controller of the first exemplary embodiment;

FIG. 6A illustrates an operation of the first exemplary embodimentduring skew amount detection;

FIG. 6B illustrates an operation of the first exemplary embodimentduring rough adjustment;

FIG. 6C illustrates an operation of the first exemplary embodiment afterthe rough adjustment;

FIG. 6D illustrates an operation of the first exemplary embodimentduring fine adjustment;

FIG. 6E illustrates an operation of the first exemplary embodimentduring side shift correction; and

FIG. 7 is a flowchart of skew correction and side shift operations ofthe first exemplary embodiment.

DETAILED DESCRIPTION

An exemplary embodiment of the present disclosure is described withreference to the drawings. The exemplary embodiment of the presentdisclosure is not limited to the following exemplary embodiment.

To facilitate understanding of the following description, the drawingsillustrate a fore-and-aft direction as an X-axis direction, a lateraldirection as a Y-axis direction, and a vertical direction as a Z-axisdirection. In the drawings, directions or sides indicated by arrows X,−X, Y, −Y, Z, and −Z are defined as “forward”, “rearward”, “rightward”,“leftward”, “upward”, and “downward”, or “front side”, “rear side”,“right side”, “left side”, “upper side”, and “lower side”, respectively.

In the drawings, a symbol represented by a dot in a circle means anarrow from back to front on the drawing sheet, and a symbol representedby a letter “x” in a circle means an arrow from front to back on thedrawing sheet.

In the following description with reference to the drawings,illustrations other than members necessary to facilitate understandingare omitted as appropriate.

First Exemplary Embodiment

FIG. 1 illustrates an overall image forming apparatus of a firstexemplary embodiment.

FIG. 2 is an enlarged view of a visible image forming device of thefirst exemplary embodiment.

In FIG. 1 , a copying machine U that is an example of an image formingapparatus includes a user interface UI that is an example of anoperator, a scanner U1 that is an example of an image reading device, afeeder U2 that is an example of a medium feeding device, an imageforming unit U3 that is an example of an image recording device, and amedium processing device U4.

(User Interface UI)

The user interface UI includes input buttons UIa to be used for startingcopying and setting the number of copies. The user interface UI furtherincludes a display UIb that displays information input by using theinput buttons UIa and the status of the copying machine U.

(Feeder U2)

In FIG. 1 , the feeder U2 includes a plurality of paper feed trays TR1,TR2, TR3, and TR4 that are examples of a medium container. The feeder U2further includes a medium feed path SH1 along which recording paper Sthat is an example of an image recording medium is picked out from anyone of the paper feed trays TR1 to TR4 and transported to the imageforming unit U3.

(Image Forming Unit U3 and Medium Processing Device U4)

In FIG. 1 , the image forming unit U3 includes an image recorder U3 athat records an image on the recording paper S transported from thefeeder U2 based on a document image read by the scanner U1.

In FIG. 1 and FIG. 2 , a latent image forming device driving circuit Dof the image forming unit U3 outputs, based on image information inputfrom the scanner U1, driving signals to yellow (Y), magenta (M), cyan(C), and black (K) latent image forming devices ROSy, ROSm, ROSc, andROSk at preset timings. Photoconductor drums Py, Pm, Pc, and Pk that areexamples of an image carrier are disposed below the latent image formingdevices ROSy to ROSk that are examples of a writer, respectively.

The surfaces of the rotating photoconductor drums Py to Pk are uniformlycharged by charging rollers CRy, CRm, CRc, and CRk that are examples ofa charger, respectively. Electrostatic latent images are formed on thecharged surfaces of the photoconductor drums Py to Pk by laser beams Ly,Lm, Lc, and Lk that are examples of latent image writing light andoutput from the latent image forming devices ROSy to ROSk, respectively.The electrostatic latent images are developed into yellow (Y), magenta(M), cyan (C), and black (K) toner images that are examples of a visibleimage by developing devices Gy, Gm, Gc, and Gk that are examples of adeveloping unit, respectively.

In the developing devices Gy to Gk, developers consumed by developmentare supplied from toner cartridges Ky, Km, Kc, and Kk that are examplesof a developer container, respectively. The toner cartridges Ky to Kkare removably mounted on a developer supply device U3 b.

The toner images on the surfaces of the photoconductor drums Py to Pkare sequentially transferred and laid over one another in first transferareas Q3 y, Q3 m, Q3 c, and Q3 k on an intermediate transfer belt B thatis an example of an intermediate transferrer by first transfer rollersT1 y, T1 m, T1 c, and T1 k that are examples of a first transferrer,respectively. Thus, a color toner image that is an example of amulticolor visible image is formed on the intermediate transfer belt B.The color toner image is transported to a second transfer area Q4.

In a case of black image information alone, the black photoconductordrum Pk and the black developing device Gk are used to form a blacktoner image.

On the photoconductor drums Py to Pk after the first transfer, drumcleaners CLy, CLm, CLc, and CLk that are examples of an image carriercleaner remove residues such as residual developers or paper dust on thesurfaces, respectively.

In the first exemplary embodiment, the photoconductor drum Pk, thecharging roller CRk, and the drum cleaner CLk are integrated into ablack photoconductor unit UK that is an example of an image carrierunit. In the other colors (yellow, magenta, and cyan) as well, thephotoconductor drums Py, Pm, and Pc, the charging rollers CRy, CRm, andCRc, and the drum cleaners CLy, CLm, and CLc constitute photoconductorunits UY, UM, and UC, respectively.

The black photoconductor unit UK and the developing device Gk includinga developing roller R0 k that is an example of a developer carrierconstitute a black image former UK+Gk. Similarly, the yellow, magenta,and cyan photoconductor units UY, UM, and UC and the developing devicesGy, Gm, and Gc including developing rollers R0 y, R0 m, and R0 cconstitute yellow, magenta, and cyan image formers UY+Gy, UM+Gm, andUC+Gc, respectively.

A belt module BM that is an example of the intermediate transferrer isdisposed below the photoconductor drums Py to Pk. The belt module BMincludes the intermediate transfer belt B that is an example of theimage carrier, a driving roller Rd that is an example of an intermediatetransferrer driver, a tension roller Rt that is an example of a tensileforce applier, a walking roller Rw that is an example of a meanderingpreventer, a plurality of idler rollers Rf that are examples of a drivencomponent, a backup roller T2 a that is an example of a facingcomponent, and the first transfer rollers T1 y to T1 k. The intermediatetransfer belt B is supported while being rotatable in an arrow Yadirection.

In the first exemplary embodiment, the yellow, magenta, and cyan firsttransfer rollers T1 y, T1 m, and T1 c are supported while beingapproachable to or separable from the photoconductor drums Py, Pm, andPc, respectively. In multicolor printing, the yellow, magenta, and cyanfirst transfer rollers T1 y, T1 m, and T1 c approach the photoconductordrums Py to Pc, respectively, to nip the intermediate transfer belt B ata predetermined contact pressure. In monochrome printing using blackalone, the first transfer rollers T1 y, T1 m, and T1 c are separatedfrom the photoconductor drums Py to Pc, respectively.

A second transfer unit Ut is disposed below the backup roller T2 a. Thesecond transfer unit Ut includes a second transfer roller T2 b that isan example of a second transferrer. The second transfer area Q4 is anarea where the second transfer roller T2 b is in contact with theintermediate transfer belt B. The backup roller T2 a faces the secondtransfer roller T2 b across the intermediate transfer belt B. A contactroller T2 c that is an example of a power supplier is in contact withthe backup roller T2 a. A second transfer voltage having the samepolarity as a toner charging polarity is applied to the contact rollerT2 c.

The backup roller T2 a, the second transfer roller T2 b, and the contactroller T2 c constitute a second transferrer T2.

The second transfer unit Ut of the first exemplary embodiment isapproachable to or separable from the intermediate transfer belt B.Depending on the type of the recording paper S in use, the secondtransfer unit Ut moves to change the contact pressure between the secondtransfer roller T2 b and the intermediate transfer belt B. For example,in a case of thick paper, the contact pressure is reduced compared witha case of plain paper to reduce an impact when the leading edge of thethick paper enters the second transfer area Q4.

A medium transport path SH2 is disposed below the belt module BM. Therecording paper S fed through the medium feed path SH1 of the feeder U2is transported to registration rollers Rr that are an example of atransport timing adjuster by transport rollers Ra that are an example ofa medium transporter. The registration rollers Rr transport therecording paper S downstream in synchronization with a timing when thetoner image formed on the intermediate transfer belt B is transported tothe second transfer area Q4. The recording paper S sent out by theregistration rollers Rr is guided by a registration paper guide SGr anda pre-transfer paper guide SG1 and transported to the second transferarea Q4.

The toner image on the intermediate transfer belt B is transferred ontothe recording paper S by the second transferrer T2 when passing throughthe second transfer area Q4. In the case of a color toner image, thetoner images firstly transferred onto the surface of the intermediatetransfer belt B and laid over one another are secondly transferredcollectively onto the recording paper S.

The first transfer rollers T1 y to T1 k, the second transferrer T2, andthe intermediate transfer belt B constitute a transfer device(transferrer) T1 y−T1 k+T2+B of the first exemplary embodiment.

The intermediate transfer belt B after the second transfer is cleaned bya belt cleaner CLB that is an example of an intermediate transferrercleaner disposed on a downstream side of the second transfer area Q4.The belt cleaner CLB removes, from the intermediate transfer belt B,residues such as paper dust or developers that remain without beingtransferred in the second transfer area Q4.

The recording paper S onto which the toner image is transferred isguided by a post-transfer paper guide SG2 and sent to a belt transportdevice BH that is an example of the medium transporter. The belttransport device BH transports the recording paper S to a fixing deviceF.

The fixing device F includes a heating roller Fh that is an example of aheater, and a pressure roller Fp that is an example of a pressurizer.The recording paper S is transported to a fixing area Q5 where theheating roller Fh is in contact with the pressure roller Fp. The tonerimage on the recording paper S is fixed by being heated and pressurizedby the fixing device F when passing through the fixing area Q5.

The image formers UY+Gy to UK+Gk, the transfer device T1 y−T1 k+T2+B,and the fixing device F constitute the image recorder U3 a that is anexample of an image former of the first exemplary embodiment.

A switching gate GT1 that is an example of a switcher is provided on adownstream side of the fixing device F. The switching gate GT1selectively switches the recording paper S having passed through thefixing area Q5 into an output path SH3 toward the medium processingdevice U4 or into a reversing path SH4. The recording paper Stransported to the output path SH3 is transported to a paper transportpath SH5 of the medium processing device U4. A curl correction member U4a that is an example of a warp corrector is disposed on the papertransport path SH5. The curl correction member U4 a corrects a warp,that is, a curl of the transported recording paper S. The recordingpaper S having undergone the curl correction is output, with itsimage-fixed side oriented upward, to an output tray TH1 that is anexample of a medium outputter by output rollers Rh that are an exampleof a medium output member.

The recording paper S transported toward the reversing path SH4 of theimage forming unit U3 by the switching gate GT1 is transported to thereversing path SH4 through a second gate GT2 that is an example of aswitching member.

To output the recording paper S with its image-fixed side orienteddownward, the transport direction of the recording paper S is reversedafter the trailing edge of the recording paper S in the transportdirection has passed through the second gate GT2. The second gate GT2 ofthe first exemplary embodiment is a thin-film elastic member. The secondgate GT2 causes the recording paper S to temporarily pass when it istransported toward the reversing path SH4, and guides the recordingpaper S toward the transport paths SH3 and SH5 when the recording paperS is reversed, that is, switched back. The switched-back recording paperS is output to the output tray TH1 through the curl correction member U4a with its image-fixed side oriented downward.

A circulation path SH6 is connected to the reversing path SH4 of theimage forming unit U3. A third gate GT3 that is an example of theswitcher is disposed at the connecting portion. The downstream end ofthe reversing path SH4 is connected to a reversing path SH7 of themedium processing device U4.

The recording paper S transported to the reversing path SH4 through theswitching gate GT1 is transported toward the reversing path SH7 of themedium processing device U4 by the third gate GT3. The third gate GT3 ofthe first exemplary embodiment is a thin-film elastic member similarlyto the second gate GT2. The third gate GT3 causes the recording paper Sto temporarily pass when it is transported along the reversing path SH4,and guides the recording paper S toward the circulation path SH6 whenthe recording paper S is switched back.

The recording paper S transported to the circulation path SH6 is sentagain to the second transfer area Q4 through the medium transport pathSH2, and printing is performed on the second side.

The elements SH1 to SH7 constitute a paper transport path SH. Theelements SH, Ra, Rr, Rh, SGr, SG1, SG2, BH, and GT1 to GT3 constitute apaper transport device SU of the first exemplary embodiment.

(Medium Transport Device)

FIG. 3 illustrates a medium transport device of the first exemplaryembodiment.

In FIG. 3 , the registration rollers Rr of the first exemplaryembodiment rotate in response to driving transmission from a motor (notillustrated) to send the recording paper S toward the second transferarea Q4, and are movable along an axial direction of each rotationshaft. Thus, the registration rollers Rr of the first exemplaryembodiment function as downstream side correction rollers that are anexample of a positional corrector and an example of a first positionalcorrection member, in addition to the function of adjusting the timingto send the recording paper S toward the second transfer area Q4.

An abutment gate 2 that is an example of a first inclination correctoris disposed at a position of first transport rollers 1 on an upstreamside of the registration rollers Rr. The abutment gate 2 is movablebetween an abutment position where an abutment portion 2 a enters themedium transport path SH2 (see the solid line in FIG. 3 ) and aretraction position where the abutment portion 2 a is retracted from themedium transport path SH2 (see the broken line in FIG. 3 ). At theabutment position of the abutment gate 2, the leading edge of therecording paper S abuts against the abutment gate 2 to correct aninclination, that is, a skew of the recording paper S.

A junction path SH6 a of the circulation path SH6 on a downstream sidein the transport direction is joined to the medium transport path SH2.The junction path SH6 a of the first exemplary embodiment is curved intoan arc from the bottom to the top. An upstream portion SH6 b extendingstraight in a horizontal direction (in a planar or flat shape) isconnected to an upstream side of the arcuate junction path SH6 a.

Along the junction path SH6 a, second transport rollers 3 that are anexample of a transporter are disposed on an upstream side of the firsttransport rollers 1 in the transport direction. Third transport rollers4 that are an example of the transporter are disposed on an upstreamside of the second transport rollers 3. In each of the first transportrollers 1 to the third transport rollers 4 of the first exemplaryembodiment, the paired rollers facing each other across the recordingpaper S are movable between a non-nipping position where the rollers areseparated from each other to cancel the nip of the recording paper S anda transport position where the rollers are in contact with each other tonip and transport the recording paper. That is, the recording paper S isnipped by each of the transport rollers 1 to 4 at the transportposition, and is not nipped at the non-nipping position. In each of thetransport rollers 1 to 4 of the first exemplary embodiment, one of thepaired rollers is a driving side and the other is a driven side. Thedriving roller does not move and the driven roller moves. In FIG. 3 ,the driving side is represented by a solid circle and the driven side isrepresented by a blank circle. In the first exemplary embodiment, theseparable roller is disposed on a lower side in the gravity direction.That is, the recording paper S sagging by gravity comes into contactwith the non-rotatable driven roller and an inappropriate transportforce is not applied to the recording paper S.

In the circulation path SH6 of FIG. 3 , upstream side correction rollers11 that are an example of the positional corrector and an example of asecond positional correction member are disposed on an upstream side ofthe third transport rollers 4. Similarly to the registration rollers Rr,the upstream side correction rollers 11 are movable along an axialdirection of each rotation shaft. The upstream side correction rollers11 also function as a medium transporter to transport the recordingpaper S downstream by nipping the recording paper S between a drivingroller 11 a and a driven roller 11 b that are examples of a mediumtransport member. Similarly to the transport rollers 1 to 4, theupstream side correction rollers 11 of the first exemplary embodimentare movable between the transport position where the recording paper isnipped by the rollers 11 a and 11 b and the non-nipping position wherethe nip of the recording paper S is canceled.

FIG. 4 illustrates a positional relationship between the positionalcorrector and the inclination corrector in the medium transport deviceof the first exemplary embodiment.

In FIG. 4 , illustration is omitted for members not related to thepositional corrector and the inclination corrector.

In FIG. 3 and FIG. 4 , skew correction rollers 21 that are an example ofa second inclination corrector are disposed in the upstream portion SH6b on an upstream side of the upstream side correction rollers 11.

In FIG. 4 , the skew correction rollers 21 are disposed in pairs with adistance therebetween in an axial direction of each rotation shaft, thatis, a width direction of the recording paper S. That is, the skewcorrection rollers 21 of the first exemplary embodiment include leftrollers 21 a that are an example of a first inclination correctionmember disposed on one side in the width direction, and right rollers 21b that are an example of a second inclination correction member disposedon the other side in the width direction. The left rollers 21 a and theright rollers 21 b of the first exemplary embodiment are independentlycontrollable in terms of driving transmission from a motor, rotationalspeed, driving and stopping, and speed change timing.

In FIG. 3 , the skew correction rollers 21 of the first exemplaryembodiment are movable between the transport position and thenon-nipping position similarly to the transport rollers 1 to 4 and theupstream side correction rollers 11. A plurality of transport rollers 31to 34 that are examples of the medium transporter are disposed on anupstream side of the skew correction rollers 21. The transport rollers31 to 34 are movable between the transport position and the non-nippingposition similarly to the transport rollers 1 to 4.

In the copying machine U of the first exemplary embodiment of FIG. 3 andFIG. 4 , a first side detection sensor SN1 that is an example of aposition detector is disposed on a downstream side of the registrationrollers Rr on the medium transport path SH2. In FIG. 4 , the first sidedetection sensor SN1 detects one edge, that is, one side of therecording paper S in the width direction. The first side detectionsensor SN1 of the first exemplary embodiment is, but not limited to, aso-called line sensor including detectors arranged in line. Any knowndetector such as a contact image sensor (CIS) may be employed to detectthe edge of the recording paper S.

A second side detection sensor SN2 that is an example of the positiondetector is disposed on a downstream side of the upstream sidecorrection rollers 11. The second side detection sensor SN2 is similarto the side detection sensor SN1 and is configured to detect one edge ofthe recording paper in the width direction.

In FIG. 3 and FIG. 4 , skew detection sensors SN3 that are an example ofa detector and an example of an inclination detector are disposed on adownstream side of the skew correction rollers 21. In FIG. 4 , the skewdetection sensors SN3 include a left sensor SN3 a associated with theleft rollers 21 a, and a right sensor SN3 b associated with the rightrollers 21 b. The inclination, that is, the skew of the recording paperS in the transport direction may be derived based on the transportspeeds of the skew correction rollers 21 and a time difference fromdetection of the leading edge of the recording paper S in the transportdirection by one of the sensors SN3 a and SN3 b to detection of theleading edge by the other one of the sensors SN3 a and SN3 b.

A paper sensor SN4 that detects the presence or absence of the recordingpaper S is disposed near the first transport rollers 1.

The rollers Rr and 1 to 34 and the sensors SN1 to SN3 constitute themedium transport device of the first exemplary embodiment.

(Controller of First Exemplary Embodiment)

FIG. 5 illustrates a controller of the first exemplary embodiment.

In FIG. 5 , a controller C of the copying machine U includes aninput/output interface I/O for inputting signals from and outputtingsignals to the outside. The controller C includes a read-only memory(ROM) that stores programs and information for processes. The controllerC further includes a random-access memory (RAM) that temporarily storesdata. The controller C further includes a central processing unit (CPU)that performs processes based on the programs stored in the ROM or thelike. The controller C of the first exemplary embodiment is a small-sizeinformation processing device, that is, a microcomputer. The controllerC may implement various functions by executing the programs stored inthe ROM or the like.

The controller C of the first exemplary embodiment receives signals fromsignal output elements, and controls control target elements byoutputting signals thereto.

(Signal Output Elements)

The controller C receives signals from the signal output elements suchas sensors (not illustrated).

(Control Target Elements)

The controller C outputs signals to the control target elements such asa power supply circuit E, a motor M1 that drives the registrationrollers Rr and the transport rollers 1 to 34, a solenoid that is anexample of a mover that moves the rollers 1 to 34 between the transportposition and the non-nipping position, and a motor M2 that moves theregistration rollers Rr and the upstream side correction rollers 11 inthe width direction of the recording paper S.

(Functions of Controller C)

The controller C of the first exemplary embodiment includes thefollowing functional elements (functional modules or program modules) C1to C6.

A paper type detector C1 that is an example of a medium type detectordetects, as examples of the type of the recording paper S, a paper typesuch as plain paper, thick paper, or thin paper and the size, inparticular, the length of the recording paper S along the transportdirection. If a user inputs the type of the recording paper (paper typeand size) via the UI, the paper type detector C1 detects information onthe input type as the type of the recording paper S. As for the size ofthe recording paper, if long paper is used and the user does not inputits paper size, the length of the recording paper S may be detectedbased on a transport speed of the recording paper S and detectionresults from sensors disposed at various positions in the transportpaths SH1 to SH7 to detect passage of the recording paper S, that is,times when the recording paper S has passed by the sensors.

A skew amount detector C2 that is an example of an inclination amountdetector detects a skew amount of the recording paper S (inclinationamount or angle relative to the transport or width direction) based ondetection results from the skew detection sensors SN3. For example, theskew amount detector C2 of the first exemplary embodiment detects theskew amount by calculating a length of deviation in the paper transportdirection relative to a unit length in the paper width direction basedon the transport speed of the recording paper S and a difference intimings when the left sensor SN3 a and the right sensor SN3 b havedetected the leading edge of the recording paper S.

A side shift amount detector C3 that is an example of a positionalcorrection amount detector detects a positional correction amount, thatis, a side shift amount in the width direction of the recording paper Sbased on detection results from the side detection sensors SN1 and SN2.The side shift amount detector C3 of the first exemplary embodimentdetects a side shift amount at the leading edge of the recording paper Sbased on the detection result from the first side detection sensor SN1.If the side edge of the recording paper S is detected by the first sidedetection sensor SN1 and the trailing edge of the recording paper S isalso detected by the second side detection sensor SN2, that is, if therecording paper S is longer than the length between the registrationrollers Rr and the upstream side correction rollers 11, the side shiftamount detector C3 detects a side shift amount at the trailing edge ofthe recording paper S based on the detection result from the second sidedetection sensor SN2.

FIG. 6A illustrates an operation of the first exemplary embodimentduring skew amount detection. FIG. 6B illustrates an operation of thefirst exemplary embodiment during rough adjustment. FIG. 6C illustratesan operation of the first exemplary embodiment after the roughadjustment. FIG. 6D illustrates an operation of the first exemplaryembodiment during fine adjustment. FIG. 6E illustrates an operation ofthe first exemplary embodiment during side shift correction.

A skew corrector C4 that is an example of an inclination correctioncontroller includes a rough adjuster C4A and a fine adjuster C4B, andcorrects a skew of the recording paper S.

The rough adjuster C4A that is an example of a second inclinationcorrection controller includes a rotational speed setter C4A1, andcorrects the skew of the recording paper S. In FIG. 6A and FIG. 6B, therough adjuster C4A of the first exemplary embodiment controls the skewcorrection rollers 21 to correct the skew of the recording paper S,thereby performing the rough adjustment that is an example of secondinclination correction.

Based on the skew amount detected by the skew amount detector C2, therotational speed setter C4A1 sets rotational speeds of the skewcorrection rollers 21 to reduce the skew amount. For example, if therecording paper S has such an inclination that the left side in thepaper width direction advances compared with the right side, therotational speed setter C4A1 of the first exemplary embodiment reducesthe skew amount by setting the rotational speed of the left rollers 21 ato be lower than the rotational speed of the right rollers 21 b. Thespeed difference between the left rollers 21 a and the right rollers 21b may be set based on the detected skew amount. The skew correction maybe performed not only by setting the rotational speeds of the rollers 21a and 21 b based on the skew amount, but also by, for example, providingtwo levels that are “high” and “low” for the rotational speeds andadjusting a timing to switch the rotational speed on the advancing sidefrom “high” to “low”, that is, a period to transport the advancing sideat a low speed based on the skew amount.

The fine adjuster C4B that is an example of a first inclinationcorrection controller corrects the skew of the recording paper S on adownstream side of the recording paper S having undergone the skewcorrection at the skew correction rollers 21. In FIG. 6D, the fineadjuster C4B of the first exemplary embodiment corrects the skew of therecording paper S by bringing the leading edge of the recording paper Sinto abutment against the abutment gate 2. That is, the fine adjustmentthat is an example of first inclination correction is performed bycorrecting the skew of the recording paper S using the abutment gate 2.In the first exemplary embodiment, the abutment gate 2 is controlled tomove to the abutment position when the recording paper S is transportedalong the circulation path SH6. The abutment gate 2 is controlled tomove to the retraction position when a predetermined period (abutmentperiod) has elapsed since the leading edge of the recording paper Sreached the abutment gate 2 based on a result of detection of theleading edge of the recording paper S by the paper sensor SN4.

A side shifter C5 that is an example of a positional correctioncontroller corrects the positions of the edges of the recording paper Sin the width direction by moving the registration rollers Rr and theupstream side correction rollers 11 in the axial direction based on theside shift amount detected by the side shift amount detector C3. In FIG.6E, the side shifter C5 of the first exemplary embodiment corrects thepositions by causing the registration rollers Rr to move (side-shift)the recording paper S in the width direction if the length of therecording paper S is smaller than the length between the registrationrollers Rr and the upstream side correction rollers 11. The side shifterC5 corrects the positions by causing the registration rollers Rr and theupstream side correction rollers 11 to move (side-shift) the recordingpaper S in the width direction if the length of the recording paper S islarger than the length between the registration rollers Rr and theupstream side correction rollers 11.

A separation controller C6 controls each of the rollers 1 to 34 to moveto the non-nipping position or the transport position during the skewcorrection or side shift operation.

To perform the skew correction (rough adjustment) using the skewcorrection rollers 21 in FIG. 6A and FIG. 6B, the separation controllerC6 of the first exemplary embodiment moves the skew correction rollers21 to the transport position and moves the transport rollers 31 to 34 onthe upstream side of the skew correction rollers 21 to the non-nippingposition

In the first exemplary embodiment, if the skew amount detected by theskew amount detector C2 has reached a predetermined amount (threshold),the upstream side correction rollers 11 are also moved to thenon-nipping position. If the skew amount has not reached the thresholdand the type of the recording paper S is a paper type easy to correctthe skew, the upstream side correction rollers 11 are kept at thetransport position. If the skew amount has not reached the threshold andthe type of the recording paper S is not the paper type easy to correctthe skew, the upstream side correction rollers 11 are moved to thenon-nipping position. In the first exemplary embodiment, examples of thepaper type easy to correct the skew include plain paper and thin paper,and examples of the paper type that is not easy to correct the skewinclude thick paper and long paper.

In the first exemplary embodiment, the upstream side correction rollers11 are moved to the non-nipping position depending on the magnitude ofthe skew amount and the paper type. Alternatively, the upstream sidecorrection rollers 11 may be kept at the non-nipping position during therough adjustment irrespective of the skew amount and the paper type in acase where, for example, the skew amount is likely to increase in viewof the structure of the circulation path SH6. Conversely, the upstreamside correction rollers 11 may be kept at the transport positionirrespective of the skew amount and the paper type in a case where theskew amount is unlikely to increase in view of the structure of thecirculation path SH6.

In the first exemplary embodiment, all the transport rollers 31 to 34 onthe upstream side are not moved to the non-nipping position, but any ofthe transport rollers 31 to 34 in contact with the recording paper S aremoved to the non-nipping position based on the length of the recordingpaper S. When the length of the recording paper S is small, only thetransport rollers 31 may be moved to the non-nipping position. When thelength of the recording paper S is large, all the transport rollers 31to 34 may be moved to the non-nipping position. Thus, when the skewcorrection rollers 21 perform the skew correction, only the skewcorrection rollers 21 are controlled to come into contact with therecording paper S, and the other rollers 31 to 34 are controlled not tocome into contact with the recording paper S. At this time, thetransport rollers 1 to 4 on the downstream side of the skew correctionrollers 21 are moved to the transport position. The rough adjustment isfinished at a predetermined timing before the leading edge of therecording paper S reaches the third transport rollers 4.

In FIG. 6C, when the rough adjustment is finished, the transport rollers31 to 34 on the upstream side of the skew correction rollers 21 aremoved to the transport position. If the upstream side correction rollers11 are at the non-nipping position, the upstream side correction rollers11 are also moved to the transport position. In FIG. 6D, the skewcorrection (fine adjustment) using the abutment gate 2 is performednext. Although the fine adjustment is performed with the rollers 1 to 34moved to the transport position in the first exemplary embodiment, thefine adjustment may be performed with the rollers 3 to 34 moved to thenon-nipping position, excluding the first transport rollers 1 near theabutment gate 2 on the upstream side.

In FIG. 6E, when the fine adjustment is finished and the side shiftoperation is started with the leading edge of the recording paper Snipped by the registration rollers Rr, the rollers other than theregistration rollers Rr and the upstream side correction rollers 11 aremoved to the non-nipping position. During the side shift operation, therecording paper S is nipped by the registration rollers Rr and theupstream side correction rollers 11.

After the position of the recording paper S is corrected by the sideshift operation, all the rollers 1 to 4, 21, and 31 to 34 at thenon-nipping position are moved to the transport position.

(Flowchart of First Exemplary Embodiment)

Referring to a flowchart, description is made about a flow of control inthe copying machine U of the first exemplary embodiment.

FIG. 7 is a flowchart of the skew correction and side shift operationsof the first exemplary embodiment.

A process of each step ST in the flowchart of FIG. 7 is performed basedon a program stored in the controller C. The process is performedparallel to various other processes in the copying machine U.

The flow of FIG. 7 is started when the copying machine U is powered ON.

In ST1 of FIG. 7 , determination is made as to whether an image formingjob has been started. If the determination result is “YES” (Y), theprocess proceeds to ST2. If the determination result is “NO” (N), ST1 isrepeated.

In ST2, determination is made as to whether the recording paper S hasreached the skew detection sensors SN3. If the determination result is“YES” (Y), the process proceeds to ST4. If the determination result is“NO” (N), the process proceeds to ST3.

In ST3, determination is made as to whether the job has been finished.If the determination result is “YES” (Y), the process returns to ST1. Ifthe determination result is “NO” (N), the process returns to ST2.

In ST4, a skew amount is detected based on detection results from theskew detection sensors SN3. Then, the process proceeds to ST5.

In ST5, the following processes (1) and (2) are executed, and theprocess proceeds to ST6.

-   -   (1) The speeds of the skew correction rollers 21 are set based        on the skew amount.    -   (2) The transport rollers 31 to 34 on the upstream side are        moved to the non-nipping position based on the length of the        recording paper S.

In ST6, determination is made as to whether the detected skew amount hasreached the threshold. If the determination result is “NO” (N), theprocess proceeds to ST7. If the determination result is “YES” (Y), theprocess proceeds to ST8.

In ST7, determination is made as to whether the type of the recordingpaper S is a paper type easy to correct the skew, that is, either plainpaper or thin paper. If the determination result is “NO” (N), theprocess proceeds to ST8. If the determination result is “YES” (Y), theprocess proceeds to ST9.

In ST8, the upstream side correction rollers 11 are moved to thenon-nipping position. Then, the process proceeds to ST9.

In ST9, determination is made as to whether the rough adjustment usingthe skew correction rollers 21 has been finished. If the determinationresult is “YES” (Y), the process proceeds to ST10. If the determinationresult is “NO” (N), ST9 is repeated.

In ST10, the following processes (1) and (2) are executed, and theprocess proceeds to ST11.

-   -   (1) The transport rollers 31 to 34 at the non-nipping position        are moved to the transport position.    -   (2) The abutment gate 2 is moved to the abutment position.

In ST11, determination is made as to whether the fine adjustment usingthe abutment gate 2 has been finished. That is, determination is made asto whether a predetermined period has elapsed since the abutment gate 2was moved to the abutment position and the leading edge of the recordingpaper S has abutted against the abutment gate 2 to finish the skewcorrection. Then, the process proceeds to ST12.

In ST12, the abutment gate 2 is moved to the retraction position. Then,the process proceeds to ST13.

In ST13, determination is made as to whether the recording paper S hasreached the side detection sensors. If the determination result is “YES”(Y), the process proceeds to ST14. If the determination result is “NO”(N), ST13 is repeated.

In ST14, the following processes (1) and (2) are executed, and theprocess proceeds to ST15.

-   -   (1) A side shift amount is detected based on detection results        from the side detection sensors SN1 and SN2.    -   (2) The rollers 1 to 4, 21, and 31 to 34 other than the        registration rollers Rr and the upstream side correction rollers        11 are moved to the non-nipping position.

In ST15, the positions of the side edges of the recording paper S arecorrected by moving (side-shifting) the registration rollers Rr and theupstream side correction rollers 11 in the axial direction based on theside shift amount. Then, the process proceeds to ST16.

In ST16, determination is made as to whether the job has been finished.If the determination result is “YES” (Y), the process returns to ST1. Ifthe determination result is “NO” (N), the process returns to ST2.

(Operations of First Exemplary Embodiment)

During duplex printing in the copying machine U of the first exemplaryembodiment having the structure described above, the recording paper Shaving an image recorded on the first side is reversed by beingtransported along the circulation path SH6. The transported recordingpaper S is sent to the second transfer area Q4 while being corrected interms of an inclination (skew) and side edge misregistration that haveoccurred during the transport. Printing on the second side is performedwith reduced misalignment of images on both sides.

In the first exemplary embodiment, the skew correction is firstperformed by the skew correction rollers 21 on the upstream side alongthe paper transport direction in the circulation path SH6. Then, theskew correction is performed by the abutment gate 2 on the downstreamside. Then, the side edge misregistration of the recording paper S iscorrected (side shift correction is performed) after the skewcorrection.

In the structure as in Japanese Unexamined Patent ApplicationPublication No. 2008-1473 in which the skew correction rollers (21, 22)perform the skew correction, the skew is corrected while transportingthe recording paper S. When the recording paper S has reached nextrollers, the skew correction is not performed any more. Therefore, thereis an upper limit on the correctable skew amount, and the skewcorrection may be insufficient in a case of a large skew amount.

The skew correction may be performed by bringing the recording paper Sinto abutment against a gate instead of using the skew correctionrollers (21, 22). In the correction by abutment, the skew at the leadingedge is corrected but the correction may be insufficient for a skew atthe trailing edge in the transport direction due to transport after thecorrection. In particular, the skew correction may become difficult asthe length of the recording paper S increases.

In the first exemplary embodiment, the skew correction is performed bythe skew correction rollers 21 on the upstream side, and then performedalso by the abutment gate 2 on the downstream side. In other words, theskew correction is performed roughly by the skew correction rollers 21on the upstream side (rough adjustment), and the final skew correctionis performed by the abutment gate 2 on the downstream side (fineadjustment).

In the first exemplary embodiment, the skew correction rollers 21 on theupstream side correct the skew by individually controlling the drivingof the rollers 21 a and 21 b on both sides in the width direction.Although an abutment gate may be provided in place of the skewcorrection rollers 21, the transport of the recording paper S istemporarily stopped by the abutment gate. Therefore, a problem arises inthat the entire transport of the recording paper S is delayed due to theabutment gates provided in two stages. In the first exemplaryembodiment, the skew correction rollers 21 perform the skew correctionwhile transporting the recording paper S downstream.

In the first exemplary embodiment, the skew is corrected by causing adifference in the transport between one edge and the other edge in thewidth direction by varying the rotational speeds of the rollers 21 a and21 b based on the skew amount. The timing to switch the rotational speedfrom “high” to “low” may be adjusted based on the skew amount.

In the first exemplary embodiment, the upstream side correction rollers11 are also moved to the non-nipping position during the skew correctionby the skew correction rollers 21 if the skew amount is large or thetype of the recording paper S is not the paper type easy to correct theskew. Therefore, if the upstream side correction rollers 11 have beenmoved to the non-nipping position, the skew is corrected by the skewcorrection rollers 21 until the leading edge of the recording paper Sreaches the third transport rollers 4. If the upstream side correctionrollers 11 are kept at the transport position and the leading edge ofthe recording paper S is nipped by the upstream side correction rollers11, the skew correction is not performed any more. If the skewcorrection is continued with the recording paper S nipped by theupstream side correction rollers 11, the recording paper S may betwisted or distorted between the upstream side correction rollers 11 andthe skew correction rollers 21 to cause damage such as creasing orripping.

In the first exemplary embodiment, during the skew correction by theskew correction rollers 21, the transport rollers 31 to 34 on theupstream side are moved to the non-nipping position. If the recordingpaper S is nipped by the transport rollers 31 to 34 during thecorrection by the skew correction rollers 21, the skew correction may behindered and the recording paper S may be creased or ripped bydistortion. In the first exemplary embodiment, during the skewcorrection by the skew correction rollers 21, the recording paper S isnot nipped by the transport rollers 31 to 34 but is nipped by the skewcorrection rollers 21 alone. In particular, in the first exemplaryembodiment, any of the transport rollers 31 to 34 to be moved to thenon-nipping position are selected based on the length of the recordingpaper S.

In the first exemplary embodiment, the skew correction rollers 21, thetransport rollers 31 to 34, and the upstream side correction rollers 11are disposed in the flat upstream portion SH6 b of the circulation pathSH6. Therefore, the skew correction is performed by the skew correctionrollers 21 with the recording paper S kept in a flat posture. In a caseof skew correction performed at a position where the recording paper Sis in a curved or wavy posture, the curved recording paper S may hinderthe skew correction by coming into contact with or interfering with thewall in the transport path, thereby causing insufficiency of correction.

In the first exemplary embodiment, the abutment gate 2 is used in thefine adjustment. During the fine adjustment, the rollers other than thefirst transport rollers 1 are moved to the non-nipping position. Whenseparating the rollers other than the first transport rollers 1, any ofthe transport rollers 3 to 34 to be separated are selected based on thelength of the recording paper S.

In the first exemplary embodiment, the side shift correction isperformed by the registration rollers Rr and the upstream sidecorrection rollers 11. In particular, in the first exemplary embodiment,the junction path SH6 a of the circulation path SH6 has an arc shape,and the registration rollers Rr and the upstream side correction rollers11 are disposed on the downstream side and the upstream side of thejunction path SH6 a. If the side shift correction is performed with therecording paper S entering the arcuate junction path SH6 a, therecording paper S may be caught and the side shift correction may beinsufficient in a case of long recording paper S. In the first exemplaryembodiment, the side shift correction is performed by the registrationrollers Rr and the upstream side correction rollers 11 disposed acrossthe junction path SH6 a.

In the first exemplary embodiment, during the side shift correction, therollers 1 to 4 and 21 to 34 other than the registration rollers Rr andthe upstream side correction rollers 11 are moved to the non-nippingposition. In particular, during the side shift correction, an outerroller 4 a disposed on an outer side of the arc in the third transportrollers 4 disposed midway along the arcuate junction path SH6 a is movedto the non-nipping position.

In the first exemplary embodiment, the upstream side correction rollers11 are disposed on an immediately downstream side of the skew correctionrollers 21. In a structure in which one or more transport members aredisposed between the upstream side correction rollers 11 and the skewcorrection rollers 21, the length of the circulation path SH6 increasesand the size of the entire device increases. Further, the transportdistance increases and a skew may newly occur.

(Modifications)

Modifications (H01) to (H05) of the exemplary embodiment of the presentdisclosure are described below.

-   -   (H01) In the exemplary embodiment, the copying machine U is        provided as the example of the image forming apparatus. The        image forming apparatus may be a FAX machine or a multifunction        peripheral having a plurality of functions of a FAX machine, a        printer, and a copying machine. The image forming apparatus is        not limited to the multicolor-development image forming        apparatus, and may be a monochrome image forming apparatus.        Further, any electronic or mechanical apparatus using motors and        gears may be an alternative to the image forming apparatus.    -   (H02) In the exemplary embodiment, the skew correction is        performed on all types of recording paper S. For example, the        rough adjustment or the fine adjustment may be skipped in a case        of thin paper or thick paper that is relatively unlikely to        cause a skew, and both the rough adjustment and the fine        adjustment may be performed only in a case of plain paper.    -   (H03) In the exemplary embodiment, the skew correction rollers        21 are used in the rough adjustment, and the abutment gate 2 is        used in the fine adjustment. The skew correction rollers may be        used both in the rough adjustment and in the fine adjustment.        The abutment gates may be used both in the rough adjustment and        in the fine adjustment. The abutment gate may be used in the        rough adjustment, and the skew correction rollers may be used in        the fine adjustment.

Although the fine adjustment and the rough adjustment are performed, therough adjustment alone may be performed without the fine adjustment orthe fine adjustment alone may be performed without the rough adjustmentif either the rough adjustment or the fine adjustment suffices in viewof the structures of the transport path and the members.

Although the skew correction is performed twice, that is, the roughadjustment and the fine adjustment are performed, the skew correctionmay be performed three times or more.

-   -   (H04) In the exemplary embodiment, the upstream side correction        rollers 11 are also used as appropriate during the side shift        correction. For example, the side shift correction may be        performed by the registration rollers Rr alone. For example, the        side shift correction may be performed by the registration        rollers Rr and the upstream side correction rollers 11 in a case        of a type of paper such as thick paper that is easily caught on        the arcuate junction path SH6 a, that is, a type of paper having        a large resistance (transport resistance) during the side shift,        and the side shift correction may be performed by the        registration rollers Rr alone in a case of plain paper or thin        paper having a small resistance during the side shift. If the        side shift correction is performed by the registration rollers        Rr alone, the upstream side correction rollers 11 are moved to        the non-nipping position.    -   (H05) In the exemplary embodiment, when the rollers are moved to        the non-nipping position, the rollers are completely separated        from the recording paper S, that is, the contact pressure with        the paper is kept zero. Alternatively, the recording paper S and        the rollers may slip on each other in such a manner that the        rollers are not completely separated from the recording paper        and the contact pressure is kept lower than that during the        transport of the recording paper.

The foregoing description of the exemplary embodiments of the presentdisclosure has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosure to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiments were chosen and described in order to best explain theprinciples of the disclosure and its practical applications, therebyenabling others skilled in the art to understand the disclosure forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of thedisclosure be defined by the following claims and their equivalents.

What is claimed is:
 1. A medium transport device comprising: aninclination corrector comprising a first inclination correction memberand a second inclination correction member disposed away from each otherin a width direction of a medium, the first inclination correctionmember and the second inclination correction member being individuallydrivable during transport of the medium, the inclination corrector beingconfigured to correct an inclination of the medium relative to atransport direction of the medium by causing a difference in thetransport of the medium between the first inclination correction memberand the second inclination correction member; and a medium transporterdisposed on a downstream side of the inclination corrector in thetransport direction and configured to transport the medium, the mediumtransporter comprising a pair of medium transport members disposedacross the medium in a thickness direction of the medium, the mediumtransport members being movable between a transport position where themedium transport members nip and transport the medium and a non-nippingposition where a nip of the medium is canceled, wherein, duringcorrection of the inclination of the medium by the inclinationcorrector, the medium transporter is moved to the non-nipping position.2. The medium transport device according to claim 1, further comprising:a detector configured to detect a magnitude of the inclination of themedium, wherein, if the detected magnitude has reached a predeterminedmagnitude, the medium transporter is moved to the non-nipping positionbefore a leading edge of the medium in the transport direction reachesthe medium transporter.
 3. The medium transport device according toclaim 2, wherein, if a type of the medium is a predetermined type ofpaper that is easy to correct and the detected magnitude has not reachedthe predetermined magnitude, the medium transporter is kept at thetransport position without being moved to the non-nipping position. 4.The medium transport device according to claim 1, wherein the differencein the transport of the medium is caused by varying transport speeds ofthe medium between the first inclination correction member and thesecond inclination correction member.
 5. The medium transport deviceaccording to claim 2, wherein the difference in the transport of themedium is caused by varying transport speeds of the medium between thefirst inclination correction member and the second inclinationcorrection member.
 6. The medium transport device according to claim 3,wherein the difference in the transport of the medium is caused byvarying transport speeds of the medium between the first inclinationcorrection member and the second inclination correction member.
 7. Themedium transport device according to claim 4, further comprising: adetector configured to detect a magnitude of the inclination of themedium, wherein the transport speeds are varied based on the detectedmagnitude.
 8. The medium transport device according to claim 5, whereinthe transport speeds are varied based on the detected magnitude.
 9. Themedium transport device according to claim 6, wherein the transportspeeds are varied based on the detected magnitude.
 10. The mediumtransport device according to claim 1, wherein the difference in thetransport of the medium is caused by varying timings to change transportspeeds of the medium between the first inclination correction member andthe second inclination correction member.
 11. The medium transportdevice according to claim 2, wherein the difference in the transport ofthe medium is caused by varying timings to change transport speeds ofthe medium between the first inclination correction member and thesecond inclination correction member.
 12. The medium transport deviceaccording to claim 3, wherein the difference in the transport of themedium is caused by varying timings to change transport speeds of themedium between the first inclination correction member and the secondinclination correction member.
 13. The medium transport device accordingto claim 4, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 14. The medium transport device accordingto claim 5, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 15. The medium transport device accordingto claim 6, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 16. The medium transport device accordingto claim 7, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 17. The medium transport device accordingto claim 8, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 18. The medium transport device accordingto claim 9, wherein the difference in the transport of the medium iscaused by varying timings to change transport speeds of the mediumbetween the first inclination correction member and the secondinclination correction member.
 19. The medium transport device accordingto claim 10, further comprising: a detector configured to detect amagnitude of the inclination of the medium, wherein the timings tochange the transport speeds are varied based on the detected magnitude.20. An image forming apparatus comprising: the medium transport deviceaccording to claim 1 configured to transport a medium; and an imageformer configured to form an image on the medium.